No convincing evidence for decline in tropical forests

Claims that tropical forests are declining cannot be backed up by hard evidence, according to new research from the University of Leeds.

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Dr Grainger does not claim that tropical deforestation is not occurring, as there is plenty of local evidence for that. But owing to the lack of frequent scientific monitoring, something for which he has campaigned for 25 years, we cannot use available data to track the long-term global trend in tropical forest area with great accuracy.

“The picture is far more complicated than previously thought,” he said. “If there is no long-term net decline it suggests that deforestation is being accompanied by a lot of natural reforestation that we have not spotted.”

Dr Grainger first examined data published every 10 years by the United Nations Food and Agriculture Organization (FAO) since 1980. These cover all forest in the humid and dry tropics and appear to indicate decline. FAO's Global Forest Resources Assessment 2000, for example, showed that all tropical forest area fell from 1,926 million hectares to 1,799 million hectares between 1990 and 2000. Ten years earlier, however, FAO’s previous report said that tropical forest area fell from 1,910 million ha to 1,756 million ha for the same 90 countries between 1980 and 1990.

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Since errors in national statistics are higher for forests in the dry tropics than for forests in the humid tropics, in places near the Equator such as Amazonia, Borneo and the Congo Basin, he repeated the process just for tropical moist forest, with a different set of data, in the hope it would give a clearer picture. This time he found no evidence for decline since the early 1970s. Indeed, while his own estimate in 1983 of tropical moist forest area in 1980 was 1,081 million hectares, the latest satellite data led to an estimate of 1,181 million hectares for the same 63 countries in 2000.

He is cautious about the apparent slight rise. “We would expect to see some increase in estimates as we use more accurate satellite sensors. This is even apparent in FAO’s data. It is sad that only in the last 10 years have we begun to make full use of the satellite technology at our disposal.”

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